1. Field of the Invention
The present invention relates generally to a gas turbine engine, and more specifically to a turbine rotor blade with cooling.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
In a gas turbine engine, such as a large frame heavy-duty industrial gas turbine (IGT) engine, a hot gas stream generated in a combustor is passed through a turbine to produce mechanical work. The turbine includes one or more rows or stages of stator vanes and rotor blades that react with the hot gas stream in a progressively decreasing temperature. The efficiency of the turbine—and therefore the engine—can be increased by passing a higher temperature gas stream into the turbine. However, the turbine inlet temperature is limited to the material properties of the turbine, especially the first stage vanes and blades, and an amount of cooling capability for these first stage airfoils.
The first stage rotor blade and stator vanes are exposed to the highest gas stream temperatures, with the temperature gradually decreasing as the gas stream passes through the turbine stages. The first and second stage airfoils (blades and vanes) must be cooled by passing cooling air through internal cooling passages and discharging the cooling air through film cooling holes to provide a blanket layer of cooling air to protect the hot metal surface from the hot gas stream. In some engines, cooling is even required in the third stage turbine blades of an IGT engine. However, the cooling requirement for the third stage blade is much less than the first and second stage blades. Some cooling is required in order to extend the life of the blade.
FIG. 1 shows a third stage turbine rotor blade for a large IGT engine will circular shaped pin fins 11 that extend across a cooling flow channel formed between the pressure and suction side walls of the mid-chord region of the airfoil. The pin fins 11 enhance the mid-chord region cooling channel internal heat transfer coefficient by 1.5 to 2 times that of an open flow channel. FIG. 2 shows a section of the pin fins 11 with cooling air flow.
FIG. 3 shows pin fins 21 having a race track shape instead of the circular shape of FIG. 2. The race track shaped pin fins will further improve the internal heat transfer performance over the circular shaped pin fins. FIG. 4 shows the cooling air flow pattern through the rows of circular pin fins 11. As the cooling air flows through the pin fin 11 bank, a turbulence level for the cooling air will gradually increase and results in an increase of the internal cooling heat transfer performance.
FIG. 5 shows the cooling air flow through the rows of race track shaped pin fins 21. As seen in FIG. 5, the race track shaped pin fins 21 provide for the cooling air flow to hit directly onto the surface of the next downstream pin fin 21. The race track shaped pin fins 21 produce a higher resistance for the cooling air flow through the pin bank compared to the circular shaped pin fins 11. The cooling air flow path becomes more tortuous. A higher turning or higher momentum change for the cooling air in-between pin fin 21 rows is produced. The overall turbulence level is increased and thus the internal heat transfer performance of the cooling air.